The invention relates to the separation of upper soil layers from the subsoil by laying a membrane of a preferably impervious material at a predetermined depth below the soil surface. This separation by underground films or membranes is done for various purposes: to produce impermeable ponds, dam levees or reservoirs for water or other liquids. Impermeable membranes are being used in the building of roads, runways, subgrades, sidewalks and road margins. More recently, impermeable membranes have been installed in agricultural fields at several decimeters below the surface with the purpose of reducing leakage of rain or irrigation water below the root zone and thus to increase the yield.
Several methods of preparing an impermeable underground layer are known. In one of these methods the soil is excavated to the necessary depth, the surface is smoothed and compacted and the impermeable layer is brought up on this surface by either laying prefabricated sheeting or by spraying a suitable plastic or liquid material. The excavated soil is then returned onto the top of the membrane. The drawbacks of this method are that the costs of smoothing and compacting after removal of the top layer are very high, that the thickness and strength of the membrane must be sufficient to sustain the stresses imposed on it by the heavy earth moving equipment used in replacing the previously removed soil, as otherwise there may be the danger of tearing, punctures and imperfect cover.
An improved method has been suggested wherein a subsoil blade is dragged through the soil parallel to the surface and simultaneously a suitable material is ejected and sprayed from the rear edge of this blade forming an impervious membrane after hardening. In this manner excavation and replacing of the soil, as well as manual or mechanical laying of a membrane are avoided and combined in one continuous operation. The main drawback of this method is the high cost of the material destined to form the membrane, since the requirement of producing a perfect continuous membrane demands the spraying of a relatively thick layer. As an example, the use of asphalt calls for a thickness of several millimeters. In addition, production of this type of membrane is limited to soils having no rough clods or aggregates and permit smooth penetration of the blade. It is also required that the soil is compatible with the sprayed material to allow perfect spraying and bonding.